The present invention relates to a method and apparatus for creating printing plates and, in particular, to the creation of multiple, simultaneously aligned plates from a single piece of printing plate stock.
Traditional methods for creating printing plates require plate makers to inventory a variety of widths and lengths of plate stock material. The specific stock sizes inventoried depend upon the width and circumference of each customer's press cylinder. Adjustments to accommodate different cylinder sizes and specific print runs compound the inventory dilemma and, more often than not, result in unusable plate stock.
Depending on the press run, the plates are typically formed from a single piece of plate stock. That is, the stock is cut into a number of separate plates of appropriate width and length to accommodate the press run. The presized plates are next separately punched to create a number of image and drum registration indices (i.e. apertures or partial apertures) which permit the alignment of the individual plates with the press cylinder and photographic equipment used to reproduce desired printing images onto the plates. At least the lead edge of each imaged plate is next formed or bent to mate with the "nose" of the cylinder and cylinder registration indices. A lockup assembly may be included with the cylinder to retain a bent portion of the tail edge of each plate to the cylinder in combination with centrifugal force.
Although generally effective in practice, the above plate preparation method produces a compounding of tolerance differentials and forming errors which can cause misalignment at the press. Not until the prepared plates are reassembled with respect to the press cylinder and the images are transferred to paper do the compounded errors become apparent. Then, the accrued error can necessitate extensive time to reset the press and re-align the plates. Overall print costs to the end-customer are thereby increased.
In appreciation of the foregoing deficiencies, Applicant has developed a method for simultaneously preparing multiple plates from a single piece of plate stock containing multiple plate images. All plates are imaged in registry to each other and the press cylinder, prior to cutting the individual plates from the stock. Plate processing time, plate stock inventory, press setup time and paper stock waste are thereby minimized.